Trichomoniasis is a venerally transmitted disease of cattle which may cause infertility, early and late abortions or uterine infections, further resulting in varying degrees of reproductive inefficiency. The causative agent for trichomoniasis is the parasitical protozoan, Tritrichomonas (Trichomonas) e.g., T. foetus.
Trichomoniasis is not a new disease but reported incidence has increased due to improved diagnostic procedures. Movement of cattle from infected areas has also expanded the incidence of the disease. Since there are no viable signs of trichomoniasis, it may go undetected until a producer becomes alarmed by such signs as cows returning to heat at the end of the breeding period, calves of varying ages and sizes at weaning, or a strung-out calving season, and, in response to such signs, the producer takes a critical look at his herd's reproductive efficiency.
The disease is highly transmissible. One infected bull results in herd infection, since a bull infects 80-90% of the cows he services. This can result in calf crop reductions as high as 40% or even more. Losses due to T. foetus infection are estimated to be in excess of $500 million annually. One hundred cow herd losses can total $16,000-$20,000.
The T. foetus is a protozoan that lives in the crypts (wrinkles or folds) on the mucosal surface of the penis and prepuce of the bull. These organisms are transmitted to the cow only by breeding. If the cow is exposed to T. foetus at the time of breeding, these tiny protozoa grow and multiply on the lining of the uterus, causing an inflammation (metritis) which eventually disrupts the placental circulation supplying nutrients to the embryo and results in death of the embryo within the first 30-60 days of pregnancy. Since the embryo is so small, the only outward sign may be a uterine infection with minimal vaginal discharge. Carrier cows do exist, which further complicates T. foetus bovine infection in cows. Typically, these chronically infected cows carry a calf to term while infected with the T. foetus organism. Clean bulls bred to carrier cows can result in the infection of the entire herd. Culling bulls will do no good so long as carrier cows remain in the herd.
The infection in the bull is completely without symptoms. Although young bulls may become infected, they are relatively resistant due to the lack of crypts on the mucous lining of the penis and prepuce. These folds in the mucous lining provide the necessary environment for the replication of the T. foetus. As a bull matures (usually at 21/2 to 3 years), these crypts become more pronounced, providing a more suitable environment for the T. foetus. While the Trichomonads grow in these crypts, they do not stimulate the bull's immune system, thus the bull remains infected.
Past attempts to immunize or vaccinate cattle against Trichomonas infection have not been very successful for a variety of reasons, including any or all of the following: 1) vaccines developed for infected bulls failed to clear or prevent infection in older bulls; 2) vaccines developed for cows failed to prevent infection in bulls; 3) vaccines developed for cows failed to stimulate local immunity in the cervico-vaginal cavity.
It is an object of the present invention to provide an effective bovine vaccine composition having high antigen load and including a very potent adjuvant which will stimulate localized mucosal immunity against Trichomonas foetus when administered systemicly to a subject bovine.
It is another object of the present invention to reduce the incidence of abortion among cows susceptible to Trichomonas infection.
It is still yet another object of this invention to increase reproductive or breeding efficiency among bovine animals (bulls and cows) susceptible to Trichomonas infection.
Yet another object of the present invention is to provide a method for preventing Trichomonas infection in cattle by immunizing these animals with an efficacious vaccine composition.
These and other objects will become more apparent in light of the detailed description which follows.